Diffusing projector lamp



v Feb. 5, 1946. R E, sMlTH 2,394,495

DIFFUSING PROJECTOR LAMP Filed Nov. 21, 1944 [/vvEA/TUR: R/EHARD E EM/THH/5 ATTUH/VEY Patented F eb. 5, 1946 mrrusmc Pnomo'ron LAMP Richard E.Smith, Cleveland Heights, Ohio, assignor to General Electric Company, acorporation of New York Application November 21, 1944, Serial No.504,434

(on. ne -a4) 3 Claims.

This invention relates to electric lamps, and.

particularly to projection lamps for diffuse illumination. The inventionis concerned with controlling the degree or angle of diffusion of thevisible or other radiation for such lamps. The invention is very usefulin connection with lamps of a general type such as disclosed in U. S.patents to Daniel K. Wright Nos. 2,148,314 and 2,148,315, grantedFebruary 21, 1939, and 2,324,972, granted July 20, 1943, commonly knownas the Sealed Beam type, and is hereinafter explained in connection withits application to such lamps. Various novel features and advantageswill become apparent from the description of species and forms ofembodiment of the invention, and from the drawing.

In the drawing, Fig. 1 shows an axial section through a sealed beam typeof lamp embodying the invention; and Fig. 2 is a side view of a diffuserslightly different from that shown in Fig. 1, on a larger scale.

Fig. 3 is a diagrammatic illustration corresponding to Fig. 1 andshowing a somewhat different type of diffuser.

A sealed beam lamp bulb or envelope I is shown in Fig. 1 as comprising arear concave pressed glass reflector portion 2 internally surfaced witha reflective metallic coating 3, and a front radiation-transmittingcover portion 4, also slightly concave and preformed out of pressedglass. The reflecting surface 3 of the rear portion 2 is shown as aparaboloid, and the front portion 4 is shown as spherical. The parts 2,4 may be separately formed out of low-expansion heat-resistant glasssuch as the borosilicate glass disclosed in U. S. Patent No. 1,304,623to Sullivan et al., known commercially as Pyrex, and may afterward besealed together by fusion at suitably mating surfaces.

Within the envelope I, at or in definite optical relation to the focalpoint 5 of the reflecting surface 3, is mounted the electricalenergy-translation means or light source which may consist of a filament6 of refractory metal extending coaxial with the reflector 3' at andthrough the focal point 5, which is preferably at mid-length of thefilament. Current connections I, 8 may be sealed through the reflector 2gas and vacuum tight as in Wright Patent No. 2,324,972, and are shown asfirst extending straight inward and as being then bent toward andparallel with one another, so that they overlap and intersect thereflector axis at opposite sides of the focal point 5. The straight endsor legs of a coiled tungsten fllament 8 are shown as welded to theoverlapping lead wire ends I, 8 with the axis of the coil coincidentwith the reflector axis at the focal point 5. As shown, the wires I, 8are interconnected, spaced, and braced together inside the reflector 2,behind the laterally bent end of the lead 1, by means comprising aninsulating length of hard or quartz glass rod 8 into whose ends arefused short wires III, III whose other ends are welded to the leads I,8.

For the purposes of the present invention, a diffuser I I is shownaround the filament coil 6. in position to intercept practically all ormost of the light from the filament that would otherwise reach thereflecting surface 3, but with its interior open into the interior ofthe envelope I. As shown in Fig. 1, the diffuser I I is of globular orelipsoid form, with opposite open ends I2, I2 coaxial with both the legsof the filament 6 and extending to the overlapping parallel portions ofthe inleads I, 8, or nearly so. The diffusing globe I I is centeredcoaxial with the filament coil, preferably with its wall substantiallyconcentric with the focal point 5. The diffuser I I may be mounted andheld in this position by means of V-bent wires I3 welded to the parallelleads I, 8 and lying in diametral planes of the ends I2, I2, whichconcurrently fit on both Vs substantially without looseness or play. Thediffuser Il may be of any light-permeable but diffusive material, suchas frosted glass, for example.

The effect of the diffuser I I is that its external surface virtuallybecomes an ellipsoidal light source so far as the reflector 3 isconcerned. Accordingly, practically every point on the reflector surface3 receives a cone of light whose vertical angle is that subtended by thediffuser I I at the point in question, or, in other words, is equal tothe angle between tangents It, It -drawn from the point to the oppositesides of the more or less elliptical outline of the diffuser II inFig.1. From each point I5 where the angle of the tangents I4, I4 is A, acone of light of the same vertical. angle A 'Is reflected, as indicatedby the lines I6, I5. To illustrate this, several such pairs of lines I4,I4 and I6, I6 have been drawn in Fig. 1 for points I5 widely separatedon the reflector surface 4. For points II far out on the reflector 3,the angle B between tangents I4, I4 and lines I6, I6 may be less than A,owing to their greater distance from the diffuser II; but it is nowheregreater than A. The direct light from the source 6 issuing through theends I2 has a much smaller angle of divergence. Accordingly, theprojector I throws a cone of light (visible or invisible) whose observedangle of divergence is the angle A. -By making the difluser ll ofsuitable size, this angle A can be made 20, 30, or practically anythingin reason that may be desired. As compared with an incandescent lamp oithe same size as the difiuser II, the candlepower maintenance oi mydevice is much better, and the light source or filament 8 can be of muchhigher wattage.

Fig. 2 shows a diffuser ll essentially very similar to that in Fig. 1,but divided into halves which are separated to afford annular opening 18between them, and without end openings as in Fig.

1. As shown. the filament c0116 extends in the general plane of thisopening, perpendicular to the axis of the associated reflector (notshown).

The opening I8 allows circulation of the atmos-. phere in the envelope Iaround the filament 6.

Fig. 3 illustrates a lamp whose envelope I may comprise reflector andlight-transmitting components more or less like those in Fig. 1.Associated with its light source 8 is a difi'user ll' somewhat differentfrom those illustrated in Figs. 1 and 2, in the form of a deep bowlenclosing the source I behind, at the sides, and to a distance forwardsuch that only a cone ofdirect light having the desired angle ofdivergence or diffusion A gets out. As in Fig. l, the diifuser llfunctions as a virtual source of illumination which subtendssubstantially the desired angle of difiusio'n or di-.

vergence A at all points ll on the reflecting surface 4, while at pointsI! the angle B is less than A. Thus the device as a whole throws a coneof light of angle A, as already explained in connection with Fig. 1. Y

In Figs. 2. and 3, various parts and features are marked with the samereference characters as those corresponding in Fig. 1, in order todispense with repetitive description.

.What I claim as new and desire to secure by- Letters' Patent of theUnited States is:

1. In a diflusing projection lamp for producing a beam of light having adesired angle of divergence, the combination of a sealed envelopecomprising a rear concave reflector portion and a front transmittingportion, a light source at the focus of the reflector, and an opendifluser in the envelope interposed between the light source and thereflector and correlated in shape with the reflecting surface to subtendsubstantially the same angle at substantially all points of the re- 3.In a diffusing projector lamp, the combination of a sealed envelopecomprising a rear concave reflector portion and a front transmittingportion, an incandescent filament in said envelope extending axially ofthe reflector at its focus, and an ellipsoidal difi'using globe in theenvelope having its major axis substantially coincident with saidfilament and having end openings opposite the ends'of said filament.

RICHARD E. SMITH.

